ooh bad head gasket = lots of work. But without jumping to conclusions, ask him why he thinks it may need a headgasket. Check the oil dipstick to see if the oil overfilled, or milky/creamy. On a cold start, have the radiator cap opened, and tell him to turn the car on for you. If bubbles start surfacing on the radiator once it starts, then thats a bad sign. Has to be a cold start though.